As an electric storage device of this type, one disclosed in Patent Literature 1 is known. Patent Literature 1 discloses an electrode assembly that is formed by winding a positive electrode plate in the form of a strip foil and a negative electrode plate in the form of a strip foil in an insulated state, with a pair of separators interposed therebetween, into a spiral shape, and flattening them, so as to have an elongated circular cross section (see FIG. 8 of Patent Literature 1, for example). An end part of each electrode of the electrode assembly is a non-coated part that is not coated with an active material, and projects from the end of the other electrode. The non-coated part is distributed at a plurality of (five) portions, and layers in the respective portions are gathered to form layer bundles. A current collector is a metal member having a plurality of grooves to receive the respective layer bundles. The layer bundles and the current collector are welded together by laser welding (see FIG. 9 of Patent Literature 1, for example).
In Patent Literature 1, the electrode assembly is depicted so that the spiral axis extends in the up-down direction. However, Patent Literature 1 fails to describe how the electrode assembly and the current collector are coupled with each other. Further, as shown in Patent Literature 2, a non-aqueous electrolyte secondary battery cell in which an electrode assembly is arranged so that its spiral axis extends in the left-right direction has been developed.
It can be understood from Patent Literature 2 that a pair of bifurcated current collectors having branched distal ends are arranged respectively at the left and right ends of the electrode assembly. However, Patent Literature 2 merely discloses an electrode assembly to an extent such that the arrangement thereof is suggested by an imaginary line. Patent Literature 2 fails to disclose how a large number of positive and negative electrode plates projecting laterally are coupled with the current collectors.